Thanks everyone, In response to: Does it hum without an input plugged up?
Yes
I will check the caps you suggested. Thanks.
I have adjusted the hum control, and it has not cured the problem.
It sounds like 60 cycle to me, maybe a bad diode or 2?

Psycho, the hum control helped. But not the solution. As far as your other concerns, I am an electronics tech in the telephony industry, and am aware of the dangers of 500+ volts. I also have been a working musician for 20 years. I just feel like this problem is something simple like the caps you mentioned. I'll try that, and let you know.

Psycho, definately no negativity drawn here from your safety concerns. I have similar mantra's that I deliver on subjects that I am more at home with (like "whoa! never say that to your pregnant wife").
It sounds like you have more tube experience than I do, and I appreciate you taking the time to offer suggestions. I will definately check the caps in question. So let it be written...